1. The Field of the Invention
This invention relates generally to grinding. More specifically, the present invention enables the efficient micronization of a wide variety of highly abrasive materials, with significantly less wear and damage to the micronizing mill, at a lower cost, and with significantly improved results over existing micronizing processes, as well as improved particle size distribution for less abrasive materials.
2. Background of the Invention
The state of the art in mills for grinding or micronizing various materials is generally characterized by milling machines that suffer significant wear when grinding abrasive materials, cannot grind abrasive materials with any degree of practicality, have poor particle size distributions, or are expensive processes that do not justify the means for grinding. Accordingly, such abrasive materials are only ground at great expensive, or not ground at all.
For example, jet mills are able to grind abrasive materials. However, jet mills require expensive and power hungry compressors that accelerate particles of the material to be ground so that the particles are caused to collide against each other in high speed streams. The impact of the particles against each other causes the particles to break down in size, with repeated circulation through the colliding streams eventually resulting in the desired particle size. Unfortunately, one of the great disadvantages of jet mills is that they require a substantial amount of energy to operate, thus making the cost of grinding abrasive materials prohibitive. Another disadvantage of jet mills is the relatively small volume of material that can be micronized.
Other mills that can be used for grinding include more conventional designs such as ball mills as shown in U.S. Pat. No. 5,769,339 issued to Karra, or a grinding mill as shown in U.S. Pat. No. 5,791,571 issued to Hijikata. Disadvantageously, both of these mills poorly handle the grinding of highly abrasive materials. The most obvious effect of grinding highly abrasive materials is that components of the mills wear excessively, to the extent that they must be stopped after only minutes of grinding in order to replace the worn components. Because of the speeds at which these grinding mills operate, and the nature of the components, the time it takes for the mills to come to a halt may be longer than the time the mills was grinding the abrasive materials.
Another disadvantage of the ball mill design is that the particle size distribution is poor. For example, consider a standard ball mill that micronizing to 200 mesh. The ball mill will typically only obtain 50% of the volume at 20 micron minus. The larger particles will either have to be sent through the ball mill again, or used for some other purpose.
Regarding wear of the mills, the grinding balls of the ball mill are worn down excessively by highly abrasive materials, resulting in the need to replace the balls often. Likewise in grinding mills, rotating bars are quickly worn down. As the rotating bars wear down at different rates, the grinding mill quickly becomes unbalanced. An unbalanced mill jeopardized bearings and other components. It is therefore necessary to stop the mill, and then replace all of the rotating bars at the same time. If they are not replaced together, then the older bars will quickly wear down, again resulting in the unbalanced load after a short time.
Accordingly, there is a great need in the grinding and micronizing industry for a milling, grinding or micronizing machine (hereinafter a micronizing milling machine) that can handle abrasive materials cost efficiently. In other words, the micronizing milling machine should be capable of operating for relatively longer periods of time between maintenance stops, it should not consume the quantity of energy of a similarly sized jet mill, and should be capable of micronizing a larger volume of material in the same amount of time. Of course, such a micronizing milling machine should therefore also perform well with less abrasive materials. The benefits should include cost savings because of reduce energy usage and less frequent replacement of components, time savings because the micronizing milling machine should not have to be stopped for maintenance as often.
It would therefore be an advantage over the prior art to provide a micronizing milling machine that could grind highly abrasive materials for longer periods of time before stopping for maintenance, could grind highly abrasive materials more cost efficiently, could grind less abrasive materials more effectively, and would have improved particle size distribution
It is an object of the present invention to provide a micronizing milling machine that can grind highly abrasive materials.
It is another object to grind highly abrasive materials using a micronizing milling machine that would require significantly less maintenance than other types of milling machines would require when grinding these materials.
It is another object to provide the micronizing milling machine that can grind highly abrasive materials while using less energy than jet mills.
It is another object to provide the micronizing milling machine that reduces wear to components while rotating at higher speeds than other rotating milling machines.
It is another object to provide components for the micronizing milling machine that wear longer, and do not have to be as precisely balanced when installed.
It is another object to provide the micronizing milling machine such that it can be scaled for construction in different sizes, depending upon the volume of material that needs to be milled.
It is another object to provide the micronizing milling machine such that it is capable of automatic load balancing.
It is another object to provide the micronizing milling machine such that it can support automated feeding of raw materials to a grinding chamber, and provide a means for retrieving the milled materials.
It is another object to provide the micronizing milling machine such that it includes a means for protecting rotating components while the highly abrasive material is fed into the grinding chamber.
It is another object to provide the micronizing milling machine such that it obtains a high percentage of micronized material at the desired particle size.
In a preferred embodiment, the present invention is a system which comprises a micronizing milling machine used for the grinding of highly abrasive materials, wherein the micronizing milling machine includes a grinding chamber having a hub and a plurality of beater bars disposed around the hub, wherein the hub rotates, thereby causing the beater bars to grind highly abrasive materials that are fed into the grinding chamber by being poured over a central cone disposed over the hub, thereby directing the highly abrasive material away from the hub, wherein the micronizing milling machine is operated at high speeds by using a load balancer to reduce vibration and prevent excessive wear of the moving components, and wherein the micronizing milling machine obtains a high percentage of material at a desired particle size.
In a first aspect of the invention, beater bars are provided which are able to withstand significant abrasion before needing repair or replacement.
In a second aspect of the invention, the load on the beater bars is balanced using a load balancing sensor which enables a load balancer coupled to a shaft of the micronizing milling machine to adjust the load and prevent damage to bearings and other components.
In a third aspect of the invention, a first cone is used to deliver abrasive material to the beater bars, and a second cone is disposed over the first cone to prevent abrasive material that is not yet milled from leaving the housing of the micronizing milling machine through an inlet passage.
In a fourth aspect of the invention, the micronizing milling machine can be operated at a substantially faster rate of rotation relative to other rotating mills.
In a fifth aspect of the invention, the beater bars include a hardface that enables the beater bars to operate for longer periods of time without replacement when micronizing organic and other highly abrasive materials.